Photo-electric means for reproducing sound from graphical records



I R. HART PHOTO ELECTRIC MEANS FOR REPRODUGING SOUND FROM GRAPHICAL RECORDS Filed Oct. 27.1924

. Nov. 1,1927.

Jttormy,

Patented Nov. 7 1, 1927-.

UNITED STATES RUSSELL HART, OF LOS ANGELES, CALIFORNIA.

Application filed. October 27, 1924. Serial No. 746,236.

In this specification and the accompanying drawing, I shall describe and show a preferred form of my invention, and specifically mention certain of its more important objects. I do not limit myself to the forms disclosed, since various changes and adaptations may be made therein without departing from the essence of my inventlon as hereinafter claimed; and objects and advantages, other than those specifically mentioned, are included within its scope.

My invention relates to photo-electric means for reproducing sound from graphical sound records. In a general way it may be said that its objects are to improve the quality or fineness of reproduction of sound from such records, above that obtainable by hitherto developed means. In the case of mechanical reproduction of sound from phonographic records a. heavy blunt needle I is unable to accurately p1ck out and respond to the very delicate and rapidly occurring undulations corresponding to the higher frequency overtones. The quality of the repro-' duced sound is changed by the blurring or partial omission of the overtone reproduction} If a light and sharp needle is used the overtones are more fully represented and the quality of the reproduction is improved unless adversely affected in other respects. In an analogous manner it is the principal object of the present invention to fully reproduce sound from graphical records, without blurring or distorting the finest overtones represented, o

More specifically, and in addition, my principal objects are; first, to provide sound reproducing'means that are responsive to ex ceedingly small variations in graphical sound records;second, to furnish facilities for clearly difierentiating periodicity in reproducing from such a record, so that the influence of the highest overtones will not be lost or distorted; third, 'to reduce the amount of light that has been required hitherto for photo-electric sound reproduction; and, fourth, to obtain the above results by means of apparatus ofgreat simplicity and relatively low cost.

My invention is particularly adapted for the reproduction of sound from photographic film records, but may be used also for reproducing other graphical sound records.

. I preferto use a photographic film record of substantially constant density and variable width, but a film having a record .of

OFFICE.

uniform width and variable density may be I used with practically equal facility.

The objects of the invention are attained in the manner illustrated in the accompanying drawing, in which- Figure 1 is a diagram showing a typical arrangement of my apparatus for reproducing sound from a photographic film record;

Figure 2 is a front elevation of a portion of a photographic film with a sound record thereon; and the gate through which it is made to slide and by which it is definitely positioned Figure 3 is a longitudinal section of the above gate and film;

Figure 4 is a rear sectional elevation of a preferred type of photo-electric cell I employ with my apparatus; and

ili igure 5 is a side elevation of the above ce Similar reference numerals refer to similar parts throughout the several views.

As illustrated, thesound record 6 consists of a photo-exposed and developed area of substantially uniform density and very variable width,'appearing asa relatively narrow longitudinal band parallel to, and near one,

edge of, a motion picturegfilm 7. It is usually preferable to have the outer edge 8 of this record rectilinear, and this edge may then be considered to represent the axis of abscissae of a' very irregular curve 6 corresponding to the recorded sound wave. The ordinates of the curve maybe considered to represent volume of sound, or loudness, and the distance between peaks, or corresponding points on the curve, correspond to pitch.

The overtones and fundamentals of the recorded'sound determine the shape of curve 6. In prior applications for United States Patents No. 608,499 filed Dec. 22, 1922 and No. 630,870 filed Apr. 9, 1923, I have shown and described means for producing such a sound record on a uniformly moving photographic film, and the recording process need' not be described herein since ithas nothing to do with the present invention.

The type of photographic film record-described or a similarly produced type having a record of uniform width and variable den sity, is made to travel for-reproducing urposes at the recording speed throug a gate 9. This may be accomplished by driving the film sprocket 10 by means of a motor 11, the film being unwound from reel 12 and re-wound upon reel 13. Figure l is diagrammatic rather than pictorial, and does not illustrate the mechanism by which reel 13 is driven to accomplish the re-winding. Such means, however, are well known to those familiar with themotion picture and allied arts. I

A source of light 14, preferably but not necessarily in the form of a luminous filament of substantial thickness, parallel to the plane of the film, and at right angles to its direction of motion, is mounted upon an adjustable clamp 15 so that the filament may be accurately positioned opposite an aperture 16 in gate 9. Rays from the light source pass through aperture 16, the sound recorded portion of film 7 a rear aperture 17 in the gate, and thence through a lens system 18 by means of which they are focused upon a photo-electric cell 19. The focusing is carefully and accurately done to form very sharp image of the sound record upon the plane of the cell. The .cell is mounted upon an adjustable clamp 20 so thatit may be accurately positioned.

The photo-electric cell I use with this apparatus is shown enlarged in Figs. 4: and 5.

In its bestform it comprises a thin plate 21 of quartz on which a thin strip 22 of platinum has been deposited. Subsequently a' film of silver is deposited upon the platinum and connecting wires 23 are soldered to this. The metallic strip is then trans versel divided by a very narrow rectilinear scratc and the latter is filled with selenium or other suitable photo-electric material bridging across the severed ends of the platinum strip. There is thus produced a very tenuous bridge 24 of photo-electric substance 1n electrical contact with a conductor at each side. Finally a cup 25. containing anhydrous calcium chloride is sealed to the quartz plate enclosing the selenium filled'scratch.

. A process for making an exceedingly sensitive and rapid photo-electric cell of the above described type has been fully. described in United States Patent No. 1,491,040 issued to me on April 22, 1924 and the process is not )laimed herein.

In operation the apparatus is assembled and adjusted so that filament 14, apertures 16 and17, 1enses 18, and selenium bridge 24, are in accurate alignment along the axial line 26. The luminous, filament and selenium bridge are also adjusted parallel to each other and to the apertures in the gate. Lenses "18 are then adjusted to accurately focus an image-of the sound record upon the plane of the selenium bridge.

With the above adjustments properly made a constantly varying amount of light,

' corresponding to variations in the sound record, will be transmitted by the film as it passes the gate apertures. This varying light flux, focused upon the selenium bridge, will proportionately vary the electrical re-' sistance of the latter, and thus make it possible to reproduce the original sound by' telephonic means. r

There are various well known means for amplifying a small electric current, modulated by the action of a photo-electric cell,. to make it available for operating loudspeaking devices. One method of doing this is illustrated diagrammatically in Fig. 1 wherein certain standard electrical devices are conventionally shown. In this diagram a loud-speaking instrument is indicatedat 27 an auclion at 28, a. variable ratio transform-er at 29, and a variable resistance at 30. The diagram'shows a satisfactory manner for connecting these devicesto batteries 31 and 32, with my photo-electric cell 19 in j circuit in the system.

I desire to point out that 'onlythat portion of the light transmitted througn the sound record which actuall 'falls upon the selenium bridge has any e ect upon the reproduced sound. This bridge is very. tenu ous (preferably not over one thousandth of an inch in width) and thus. makes it possible to reproduce sound with extremeaccuracy and fidelity as to quality. There is practiu cally no blurring of the sound due to overlapping the elfects of adjacent portions of the sound record. i

The use of quartz upon which to deposit the photo-active material of the cell is desirable on account of the optical qualities of this substance, and also because its 'co-etiicientof expansion is very small or negligible.

' Having thus fully described my invention I claim:

1. Photo-electric sound reproducing means comprising; a source of light; a movable optical film with a sound record thereon adapted for modulating rays transmitted.- from said source; a rectilinear photo-elem v tric bridge of relatively great tenuity disposed parallel to the plane-of said film transversely to its direction of motion and exposed to the action of said modulated rays; and a lens intermediate said record and said bridge whereby an image of the former may be focused upon the latter.

2. Photo-electric sound reproducing means comprising; a source of light; a movable optical film with a sound record thereon adapted for transmitting modulated rays focused upon the latter; and facilities for reproducing the motion. of the film when said record was made thereon.

3; Photo-electric sound reproducing means comprising the elements set forth.- in claim 2 in combinationwith; means for passing an electric current through said bridge for modulation thereby; and means for utilizing said modulated current for the reproduction of sound. 4. Photo-electric sound reproducing means .comprising the elements set forth in claim 2 in combination with; means for passing an electric current through said bridge for modulation thereby; and means for amplifying and telephonically utilizing said modulated current for the reproduction of sound.

5. Photo-electric sound reproducing means comprising; an illuminable, rectilinear filament; a uniformly movable optical film having a sound record thereon adapted for variably transmitting rays from said filament; a photo-electric cell having a tenuous filament of photo-electric material disposed parallel to the plane of said film transversely to its direction'of motion in the path of .saidtransmitted rays; and a lens intermediting rays from said filament; a photo-electric cell having a tenuous filament of photo-' electric material disposed parallel to the i plane of said film transversely to its direction of motion in the path of said transmitted rays; a lens intermediate said record and said photo-electric filament whereby an image of the former may be focused upon the latter; and a circuit including said photoelectric filament and telephonic sound reproducing means, whereby an electric current may be modulated by co-action of said transmitted rays and said photo-electric filament.

'7. Photo-electric sound reproducing means comprising; an illuminable rectilinear filament; a uniformly movable optical film disposed parallel to said filament and having a sound record thereon adapted for variably transmitting rays from. said filament; a photo-electric cell, having a tenuous filament of photo-electric material disposed in the.

path of said transmitted rays parallel to the plane of the film, and angularly adjustable 7 about a transverse axis; a lens intermediate said record and said photo-electric filament whereby an image or the former may be focused upon the latter; anda circuit including said photo electric' filament and amplifying. telephonic sound reproducing means, whereby an electric current may be modulated by coeaction of said transmitted rays and said photo-electric filament.

8. Photo-electric sound reproducing means comprising; an illuminable rectilinear filament having means for angularly adjusting its position about a transverse axis; a uniformly movable optical film disposed paral-' lel to said filament and having a sound record thereon, adapted for variably transmitting rays from said filament; a photoelectric cell, having a tenuous filament of photo-electric material disposed in the path of said transmitted rays parallel to the plane of said film and angularly adjustable about a transverse axis; a lens intermediatesaid record and said photo-electric filament whereby an image of the former may be focused upon the latter; a circuit including said photo-electric filament whereby an electric current may be modulated by co-action of said transmitted rays and said photoelectric filament; means for amplifying said modulated current; and telephonic apparatus whereby said amplified current may be made to reproduce sound.

RUSSELL HART. 

